Synthetic plastics have made great contributions to promoting industrial development and improving people's living standards. In the early stage of the development of the plastics industry, the chemical stability of synthetic materials was one of the contents that people were very concerned about and focused on. Decades have passed, and its stability has been well resolved. What is dramatic is that its stability today has become an important reason hindering its further development. "Agricultural film" is a good example. Because it is difficult to be biodegraded, it can only be used once, and the simple way to deal with it is to burn it. This not only wastes resources, but also causes air pollution.
The recycling and utilization of waste plastic products has become a worldwide issue. Traditional landfill and incineration treatment methods are gradually being replaced by reuse, degradation or decomposition processes. The recycling of waste plastic products can not only protect the environment and save energy, but also has good economic efficiency.
The industry has three concepts for the recycling and utilization of plastic products, namely, direct utilization, conversion utilization and incineration or biological decomposition.
Conversion use, as the name implies, is to use it for other purposes. Contains both chemical and physical methods.
Chemical methods can be divided into two types: One method is to use the chemical properties of polymers to convert polymers into small molecular compounds or simple compounds. For example, polyester can be converted into monomers or small molecule compounds by hydrolysis, alcoholysis or aminolysis. The hydrolysis reaction is the reverse reaction of the polyester synthesis reaction, which can be made into terephthalic acid and ethylene glycol (polyester synthetic raw material monomer); methanol alcoholysis can produce methyl terephthalate and ethylene glycol; glycol alcohol The product of the solution is bishydroxyethyl terephthalate; the alcoholysis of propylene glycol produces oligomers, which are used to synthesize unsaturated polyesters (for paints or inks) and alkyd resins.
Another method is to use the flammability of plastics to generate heat to generate electricity after incineration. These two methods have their own advantages and disadvantages. The chemical decomposition method has a high utilization rate of resources, but the process is complicated and the cost is high, which affects the recycling of plastic products. The waste gas from incineration, such as the chlorine-containing gas produced by the combustion of PVC (polyvinyl chloride film), is a component of acid rain. In addition, many plastics produce waste gas due to incomplete combustion, which is very harmful to the environment and human health. This method has a tendency to be eliminated.